Soap is an efficient cleaning surfactant which has been used historically in toilet bar compositions. Because soap can be harsh on the skin, however, for many years it has been sought to find a milder (i.e., less harsh) surfactant which can be used together with or in place of soap in such toilet bar compositions. U.S. Pat. No. 4,695,395 to Caswell et al., for example, teaches a toilet bar composition comprising both soap and acyl fatty isethionate and which composition is substantially milder to the skin then pure soap.
In such non-soap detergent active bars, free fatty acid is generally used to structure the bars (i.e., keep them from physically falling apart).
Fatty acids, however, are not the only materials which can be used to provide bar structuring. In U.S. Ser. No. 08/148,120 to Massaro et al., for example, applicants teach that polyalkylene glycol is a preferred structurant, at least when used with aldobionamide surfactants, because they provide good structuring characteristics without simultaneously inhibiting lather formation.
In another copending application, i.e., U.S. Ser. No. 08/213,287 to Chambers, applicants teach compositions comprising 10-60% of a synthetic non-soap surfactant as well as 10-60% of a water soluble structurant having a melting point in the range of 40.degree.-100.degree. C. A preferred structurant is said to be a polyalkylene glycol such as polyethylene glycol.
The use of polyalkylene glycol structurant, while beneficial, often comes at the expense not only of fatty acid (if at all), but also of the non-soap surfactant. When the non-soap surfactant is, for example, directly esterified isethionate (e.g. DEFI), this can be detrimental because DEFI in itself has a stabilizing effect on the composition (i.e., helps to stop compositions from phase separating).
Thus, the use of polyethylene glycol and the simultaneous use of lower amounts of DEFI than normally used can cause the type of phase separation that makes such bars very difficult to process.
Unexpectedly, applicants have found that certain organic amide compounds (e.g., urea) interact with such PEG/lower DEFI formulations in such a way that phase separation is avoided.
Organic amides such as urea have been used in soap bar compositions such as is taught in U.S. Pat. No. 3,991,001 to Srinivasan et al.; for example, to improve lathering properties. Soap bar compositions, however, do not have the phase separation problems noted above associated with PEG/relatively low DEFI bars and there is no recognition that the organic amide could be used to stop such separation and aid in bar processing.
German Patent 2,627,459 to Twenlow (assigned to Unilever) teaches the use of amides such as urea in compositions comprising 48.6% sodium acyl isethionate (i.e., DEFI). This amount of DEFI is high enough to help in the phase formation of the bar such that there would not be the type of phase separation noted when PEG is added and the DEFI levels are lowered (i.e., to under about 40% by wt. DEFI in the detergent bar).
Unexpectedly, applicants have found that, even in bars comprising polyalkylene glycol and under about 40% by wt. DEFI, the phase separation problem otherwise seen disappears when organic amides, such as urea, are in the composition.